1. Field of the Invention
This invention relates to a trampoline for use on a swimming pool, lake or other similar body of water. More particuarly, the subject invention pertains to a flotation trampoline adapted for stable use on a water surface.
2. Prior Art
Trampoline devices are well known in sports and athletic fields. Generally, a trampoline consists of a sheet of canvas attached by resilient cords or springs to a horizontal frame several feet above the floor. Traditionally such devices have been used by acrobats and gymnasts as a spring board in tumbling activities. More recently, smaller trampoline devices have been developed for exercise techniques such as jogging.
Trampolines have characteristically been used on a solid floor base or in a ground mounted configuration. This has been required in view of the large forces which are applied to the canvas and rigid support as a person bounces and impacts the resilient canvas surface. Without the solid floor or ground for support, the trampoline would be unable to resist the force of impact of the user.
Intuitively, the efficiency of a trampoline depends in part on its ability to retain the energy of impact as the user jumps on the canvas, and store that energy for rebound. If the energy is dissipated to any significant degree, the ability of the trampoline to operate is significantly impaired. Positioning the trampoline on a hard surface minimizes the amount of energy transferred through the rigid frame and thereby enhances the efficiency of the trampoline to provide increasing rebound lift as the user jumps higher with each successive bounce.
Pneumatic trampoline devices have been developed which rely totally upon the use of a hard surface. An example of such a trampoline is U.S Pat. No. 3,130,816 by H. B. Wright. It discloses a trampoline which utilizes the collapsable response of an inner tube to provide lift in response to each bounce. Its operation depends upon the ability of the pneumatic tube to expand or balloon during impact, and thereby store this energy for subsequent rebound.
In attempting to develop the same efficiency in a flotation type trampoline, it will be apparent that serious problems will be encountered. First, a stable platform capable of floating in a water surface must be developed which is capable of retaining stability despite extreme impacts which occur during use. Because of the low friction factor at the water surface, energy dissipation can occur in multiple directions. The most obvious direction of energy loss is along the vertical line of movement of the user. For example, as the person jumping on the trampoline impacts the canvas mat, the trampoline is driven deeper in the water. If the trampoline mat is supported underneath by a conventional innertube, the impact of the user drives water up through the opening of the innertube. This not only dissipates rebound energy of the trampoline, but also lowers the distance of free movement between the water surface and trampoline mat. The consequence is that a trampoline support on an innertube is virtually non-functional because the displacement of water at impact absorbs most of the impacting force.
In addition to the difficulty of maintaining vertical stability for a flotation trampoline, lateral stability is difficult to maintain. If the impact of the user at the trampoline is off center, the force applied to the floating support is non-uniform. In such circumstances, the floating support will move in the direction of lateral force. The consequence is that as the user jumps on the trampoline and impacts off center, the trampoline slides over the water surface, out of alignment with the user. As a consequence, a flotation trampoline may allow one jump for the user before going out of position and being useless as far as repeated jumping is concerned.
In view of the foregoing problems, flotation trampolines have not previously been designed for repeated jumping. Instead, such trampolines function merely as diving boards positioned on the water surface. Their use consists of a single jump or bounce.
A further problem with a pneumatic type of trampoline arises from the collapsible nature of the innertube structure which is designed to provide the resilience for jumping movement. As the user impacts off center on any portion of the trampoline, the non-uniform distribution of the force over the supporting tube results in differential expansion of the tube. In other words, one portion of the tube will become more greatly enlarged, forcing the tube to move laterally in the direction of lesser expansion. Such lateral movement is the by product of the attempt of the tube to establish itself to a horizontal level in the water. Here again, lateral movement of the tube permits one bounce on the user before the tube is displaced out of the vertical direction of movement.
What is needed, therefore, is a flotation trampoline which is capable of maintaining a stable platform during repeated jumping movement, while at the same time preventing dissipation of force in either vertical or lateral directions.